1. Field of the Invention
The present invention relates to a closure liner and more specifically to a multi-layer closure liner which features gas barrier improved sealing characteristics and which includes an oxygen scavenging capacity.
2. Brief Description of the Related Art
Typically closures used in conjunction with plastic bottles are produced from commodity grade thermoplastic resins--polypropylene being presently the most popular resin due to a proper combination of physical properties and a low cost. However, such materials exhibit a relatively low resistance to permeation by gases such as air. Thus, the contents of the bottles made of this material will, irrespective of measures such as hot filling, inert gas flushing or vacuum degassing, tend to be, upon standing, exposed to atmospheric oxygen and thus subject to the possibilities of detrimental oxidation.
More specifically, oxygen which is a strong oxidizer, will chemically react with the content of the package/container and eventually will tend to make the product unusable due to chemical changes which will take place. Products which are subject to a chemical oxidation include, way of example only, foods and beverages, dyes, cosmetic products, photo chemicals and adhesives. Vitamin C is particularly susceptible to the effects of oxygen and products containing such material are prone to degradation and are apt to undergo changes in flavor, color or odor.
To overcome this drawback it has been proposed to make the bottle of a material which is less gas permeable. However, even under these circumstances, the closure member or cap can become a problem in that it is formed of a material which exhibits a lower resistance to gas permeation than the remainder of the bottle. That is to say, if a bottle or container is produced from a plastic which exhibits good gas barrier characteristics, such as PET--Polyethylene terephthalate, for example, or is made using a sophisticated multilayer material with relatively high gas barrier per unit area, then the surface area of the closure in an overall amount of the gas transmission is apt to become significant and must be given consideration.
However, due to the complexity of the process currently employed in the manufacture of plastic closures, which are mostly produced by injection molding using thermoplastic resins in multi-cavity molds, there are great technical and economical difficulties in designing a process which will allow the production of closures with suitably high gas barrier properties. Therefore, in order to reduce gas transmission rate through the closure area of the container, high-barrier liners are being used to provide a necessary seal as well as gas barrier characteristics.
Some presently used high-barrier liners are produced by the lamination of the coextruded Skin/Foam/Skin products with so-called barrier films or aluminum foil. However, this type of "passive" measure of preventing the invasion of oxygen into the interior of a container has met with only limited success and it has been accordingly proposed to actively scavenge oxygen in the head space which remains in a filled container in an effort to protect the contents of the container from the detrimental oxidizing effects of oxygen.
For example, U.S. Pat. No. 4,756,436 to Morita et al. discloses the use of a specially configured cap in which two compartments are separated from each other by a gas permeable liquid proof sheet. The lower of the two compartments contains an amount of oxygen scavenger, while the upper compartment is communicated with the head space above the liquid which is filled into the bottle, by small diameter passages. However, this arrangement while possibly being effective, is expensive to make and assemble and is not particularly suited for application with screw threads of the nature used in common plastic containers.
U.S. Pat. No. 4,287,995 to Moriya discloses a closure arrangement wherein an oxygen absorbent is disposed in a compartment which is defined below or in a layer of elastic packing material, and separated from the contents of the container by a gas permeable film. While this arrangement may be less complex and therefore less expensive to manufacture that than discussed above, it does not exact any measures which totally prevent the invasion of gas from outside of the container and therefore has not been totally successful in protecting the contents of the container from exposure to oxygen over prolonged periods of storage.
U.S. Pat. No. 4,279,350 to King teaches an oxygen scavenging system wherein a catalyst is used to convert oxygen, which has passed through a gas permeable water proof layer, into water, which is then trapped by the water proof layer. This arrangement is also devoid of measures to prevent the invasion of oxygen from outside of the vessel or container, and thus has tended to be less efficient than desired over prolonged periods of time.
U.S. Pat. No. 4,840,280 to Schvester discloses the provision of a layer of material containing an oxygen absorber and the provision of a film of polydialkyl siloxane to prevent the oxygen absorbing layers from direct contact with liquid stored in the vessel. Again there is no effort to prevent the invasion of external oxygen and only the oxygen which remains in the head space immediately after filling is considered.
Accordingly, there has not been any successful proposal of a commercially feasible low cost easy to produce liner which can be readily used in place of existing liners and which will a) prevent the ingress of oxygen containing air, and b) scavenge undesirable oxygen in the head space above the product filled into a vessel or container.